(1) Field of the Invention
This invention relates to a radiographic apparatus such as a fluoroscopic table, C-arm apparatus, X-ray CT apparatus, general photographic apparatus or the like for use in the medical or industrial field. The apparatus includes an irradiating device for emitting a penetrating electromagnetic wave in a diverging form to a patient or object under examination, a planar detecting device opposed to the irradiating device across the patient or object and having a plurality of pixels arranged in an array for detecting the electromagnetic wave transmitted through the patient or object, a moving device for moving the irradiating device and planar detecting device as synchronized with each other, and an image creating device for acquiring projection images of the patient or object irradiated by the electromagnetic wave emitted from varied directions by the action of the moving device, and performing a reconstructing calculation of the projection images of the patient or object, to create slice images and/or three-dimensional images of a selected site.
(2) Description of the Related Art
This type of radiographic apparatus requires a maintenance or calibration to be carried out, for example, when collecting images of a patient or object under examination, in time of periodical inspection or in time of inspection following a trouble. The following construction is known to meet such a requirement.
According to a conventional radiographic apparatus, a calibration phantom is placed on a top board for supporting a patient or object to be examined, and a scanning device causes the irradiating device and planar or area detector to make one scanning revolution, and a projection line of a rotation sectional axis is derived from projection images thereby obtained. To prevent generation of artifacts in slice images, the irradiating device and planar detector are required to lie on a precise circular track about the rotation sectional axis. The irradiating device and planar detector are adjusted to bring a predetermined row of pixels of the planar detector into agreement with the projection line of the rotational sectional axis (see Japanese Unexamined Patent Publication 2003-61944, for example).
With the conventional apparatus, however, a rigid calibration is impossible when the track of the irradiating device and planar detector is even slightly displaced from a precise circular track about the rotation sectional axis. Further, in order to determine the projection line of the rotation sectional axis, the irradiating device and planar detector must be revolved at least 180 degrees. With a small scan range of 40 degrees, for example, a wide range scan must be performed, resulting in a drawback of requiring time and effort for a calibration.
Further, an adjustment by movement of the planar detector must also be carried out finally. A great trouble must be taken until required images are secured.